Inorganic-Organic Barrier Coatings for Flexible OLED Applications

When flexible organic substrates are used for organic light emitting diodes (OLEDs), a barrier layer is required for the substrate to protect the enclosed functional materials from oxygen and water penetration. In this study, barrier coatings consisting of organic and inorganic films were developed for the organic substrate to ensure sufficient hermetic protection. As a model system, we chose the 'Parylene-C/TiO₂' grown on the polyethylene terephthalate (PET) substrates. Parylene C films, which were vapor deposited at room temperature, have been known for a superior conformal coverage. The oxide films were biomimetically formed from in- situ precipitated particles in aqueous solutions and displayed nanoparticulate, dense structures. Since these oxides are processed at very low temperatures (< 70degC) in aqueous solutions, the processes can be applicable to organic structures, cheap and environment-friendly. Further, plasma treatments were employed to adjust the functionality of the organic surfaces and their effects on microstructure evolution of subsequent depositing layers are discussed. In order to evaluate the mechanical properties and film adhesion of the inorganic-organic hybrid coatings, in-situ AFM coupled nanoindentation techniques were introduced. Preliminary results on the dye penetration test indicated that the hermeticity of the barrier coatings was improved by having the hybrid films consisting of parylene-C and TiO₂.